Enhancing plant growth using anaerobic co-digestate of pig manure, food waste, and coffee grounds

Abstract

This study demonstrates a novel application of anaerobic co-digestate liquid (AcoDL), derived from pig manure inoculum, food waste, and spent coffee grounds (PMI/FW/SCG), as a sustainable biofertilizer. The PMI/FW/SCG AcoDL exhibited a favorable physicochemical profile (pH 8.09, electrical conductivity 14.44 mS/cm; N–P–K: 0.16–1.23–0.15% w/w) and contained plant growth-promoting compounds such as salicylic acid, kinetin, and essential amino acids. Microbial community analysis revealed a dominance of beneficial taxa, particularly Methanothrix soehngenii (55.98%) and Propionibacterium sp. (5.76%). In hydroponic cultivation, AcoDL supplementation increased the biomass of green oak lettuce by approximately 2.7-fold (127.6 g compared with 47.9 g in the controls). In soil-based systems, the combination of AcoDL with cow manure markedly increased triterpene accumulation in Gotu Kola, with asiaticoside (71.49 mg) and madecassoside (41.55 mg) levels reaching 2–3 times higher than those in the controls. Biotoxicity assays confirmed its safety for agricultural applications. Collectively, these findings demonstrate that PMI/FW/SCG AcoDL functions as a sustainable and eco-friendly fertilizer that not only improves crop yield but also promotes the production of bioactive compounds. By converting organic waste into a high-value agricultural input, this approach advances circular waste management, reduces reliance on synthetic fertilizers, and supports sustainable crop production.